Lorch spindle pin

Hmmmm, I don't know. But on most other WW type lathes, it is a pin, and appears to be soldered in place. When I replace these, and I have on several lathes, I use hardened steel. Watchmakers blued steel pivot wire.

Soft solder?

not sure if the original pins are all that hard, it is only a guide to ensure the collet locates in the same place and doesn't rotate as you tighten or release the draw bar.

the headstock spindle is hardened steel so I would be careful not to drive in something hard and oversized.

it has been a while since I have replaced a guide pin on one of my lathes but from memory it was just a round parallel pin with the end that goes inside the spindle shaped to fit the groove in the collet (a couple of slight flats on either side).

anyway it doesn't need to be a very tight fit, just so long as it fits in without side play and the collet slides in without binding, I just loctite or studlock the pin in place

Yes, soft solder, you don't want to draw the hardness/temper from the spindle. And as dAz suggested, it does not have to be hardened steel, but consider any wear that might happen. It's just one less thing that you may have to do a second time.

It does have to fit the milled slot in your collets, however most folks have numerous brands of collets and some collets have been milled to fit the pin.

Are you somewhat curious has to how or why the pin was sheared off?

Well, yes, I suppose...

I gave the pin a bit of a tap with a punch; it moved down into the bore, and happened to be just right to slide snugly in a collet slot. There's about 3/32 of drop to the top of the pin surface from the cone surface. I went over the hole edges with a diamond file a few times to remove the little burr, and put the whole thing back together.

Thanks, all. Fell free to tell me anything I missed.